Hormones

Hormones Definition

Similar to neurotransmitters, hormones are chemical messengers within the body.

Hormones examples

As hormones are chemical messengers, many types of hormones exist within the body that target organs, cells, and tissues.

Hormones examples include:

• Adrenaline
• Melatonin
• Thyroxine
• Insulin
• Glucagon
• Testosterone
• Oestrogen
• Progesterone
• Oxytocin

Sleep acts as a reset for hormones, and naturally, certain hormones rise and decline in levels depending on when you are asleep and when you are awake.

Pineal Gland Hormones

The pineal gland is located behind the third cerebral ventricle between the two hemispheres in the brain. It is shaped somewhat like a pinecone (hence the name).

It is an endocrine gland. Endocrine glands are part of the endocrine system, which releases hormones to perform different functions. The hormones travel around the body via the circulatory system and bind to their preferred receptors when they meet the target cell.

The pineal gland produces melatonin. To understand the role melatonin plays in our sleep, we need to know about bodily rhythms, specifically the circadian rhythm, on which the sleep-wake cycle operates.

The Sleep-Wake Cycle Summary

The body operates on internal rhythms (biological clocks), and the sleep-wake cycle is part of the circadian rhythm, a daily rhythm. It is a 24-hour cycle which affects the body's temperature, sleep, feelings of wakefulness, and even hunger.

When we are approaching the end of the day, and it's time to sleep, the body temperature drops, light levels are low, and our internal clock readies us for sleep. The sleep cycle (the four stages of sleep and REM sleep) is an example of an ultradian rhythm (a rhythm that lasts less than 24 hours).

The sleep-wake cycle operates on a 24-hour cycle, freepik.com/redgreystock

Melatonin Hormone Function

Melatonin is the sleep hormone. It is produced when it is dark to signal the time for sleep. As discussed above, the circadian rhythm is what the sleep-wake cycle operates on, which is intrinsically linked to melatonin. It acts as a trigger in the circadian rhythm, synchronising it to the time and waking hours as a natural clock.

Melatonin levels increase in the evening to trigger sleep and reduce towards the end of sleep to allow you to wake up.

Melatonin operates on light and darkness, so we may have problems with our sleep-wake cycle when we artificially affect these scenarios.

Jet lag and seasonal affective disorder (SAD)

Jet lag happens when a person travels from one place to another that has different time zones, usually via plane. Planes are the fastest form of travel over long distances.

When travelling to a place several hours behind the local time of the place you're leaving, you will tend to feel tired earlier than the time that locals to the destination would sleep.

Feelings of depression characterise seasonal affective disorder (SAD). It seems to affect most in the winter, and people with SAD often have issues with a lack of energy, difficulty concentrating, and general feelings of sadness, guilt, and hopelessness.

The circadian phase-shift hypothesis suggests that the stages or phases of the sleep-wake cycle shift in the day, which causes a circadian misalignment. When this misalignment is corrected by providing doses of melatonin, symptoms of SAD improve, as it causes phase delays or phase advances depending on the misalignment (Lewy et al., 2006).

It is also suggested that people with SAD have issues with overproduction of melatonin, which induces feelings of tiredness, sleepiness, and a lack of energy those with SAD feel.

Both jet lag and SAD can be treated somewhat with melatonin medication.

Jet lag affects your sleep-wake cycle, freepik.com/vectorjuice